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Consider capacity and voltage level. Load type. Wait

1. First, it is necessary to determine the purpose of using frequency conversion: whether it is for constant voltage control or constant current control, etc. 2. What type of load is connected to the frequency converter? For example, it could be a vane pump or a positive displacement pump; special attention should be paid to the performance curve of the load, as this curve determines the methods by which the frequency converter should be used. 3. The issue of whether the frequency converter is suitable for the load: 1) Is the voltage matched? The rated voltage of the frequency converter must match the voltage of the load. 2) Is the current matched? For ordinary centrifugal pumps, the rated current of the frequency converter matches the rated current of the motor. However, for special loads such as deep well pumps, it is necessary to refer to the motor performance parameters in order to determine the current capacity and overload capability of the frequency converter based on the maximum current. 3) Is the torque matched? This situation can occur with constant-torque loads or when there is a reduction gear. 4. When using an inverter to drive a high-speed motor, due to the low reactance of such motors, an increase in higher harmonics leads to an increase in the output current value. Therefore, when selecting an inverter for high-speed motors, we should choose an inverter with a capacity that is slightly greater than that required for ordinary motors ； 5. If the inverter is to operate over long cables, it is necessary to take measures to mitigate the effect of the coupling capacitance between the cables and ground, in order to prevent the inverter from having insufficient output power. In such cases, the capacity of the inverter should be increased by one level, or an output reactor should be installed at the inverter’s output terminal. 6. In special situations such as high temperatures or high altitudes, these conditions can cause a reduction in the capacity of the frequency converter; therefore, the capacity of the frequency converter used in such situations should be one tier higher than that of frequency converters used in other situations.

First, check the motor’s rated power and rated current, then determine whether it is a constant-torque or variable-torque load. Also, find out what voltage is being supplied to the inverter. For the rest, consider communication, or whether to use a four-quadrant or two-quadrant approach, etc. As for brands, domestic ones are also good; inverter technology is now very mature, so there’s no need to buy expensive foreign products.

The selection of low-voltage general-purpose frequency converters involves two aspects: the choice of the type of such converter and the determination of its capacity. There are two basic principles for selecting a frequency converter: its functional capabilities must ensure the reliable fulfillment of process requirements, and it must offer a relatively good cost-performance ratio. When selecting an inverter, you can follow these six steps: 1. Determine the operating mode, capacity, and type of load of the equipment. 2. Define the process, performance specifications, and control requirements of the equipment. 3. Determine the configuration of internal systems, I/O interfaces, communication interfaces, etc. 4. Summarize the various performance indicators and requirements. 5. Provide technical consultation on the summarized results or proceed with direct bidding. 6. Conduct a comprehensive comparison of the performance of frequency converters, their service life, price, and support services.

When selecting an inverter, one should not consider only the power of the load; the current is the key factor. In general, the rated current of the selected inverter should be greater than or equal to the rated current of the load. There are two common control methods nowadays: one is the traditional V/F control, and the other is the modern vector control. The main difference between these two control methods is: first, control precision. Vector control is a type of closed-loop control, and therefore it offers higher control precision. In contrast, V/F control is an open-loop control, and its control precision is lower compared to that of vector control. Second is low-frequency torque. This mainly depends on the inertia of the load; if the load has high inertia and needs to operate at low frequencies for an extended period, a variable frequency drive with vector control should be used. By low frequency, it is generally meant frequencies of 10Hz or less. Third, vector-controlled inverters are more expensive than ordinary V/F-controlled inverters.

It is very important to select the right frequency converter; if the selection is improper, it can result in losses of money and time at the least, and production accidents or injuries to personnel at the worst. The selection of an inverter should take the following aspects into consideration: 1. Selection of inverter type. Inverters can be divided into general-purpose and specialized types; for ordinary mechanical loads and situations requiring high overload capacity, general-purpose inverters should be chosen. Specialized frequency converters can be further divided into those designed for air pumps, elevators, tension control, etc. Choose based on your own application environment. 2. Selection of inverter capacity: The selection of the inverter’s capacity is of utmost importance; it should be determined based on the actual load current, starting torque, and control method of the load. If the load is a fan or water pump, choose a model designed specifically for fans, with a power rating equal to that of the motor ； For Roots blowers and deep well pumps, a frequency converter designed specifically for air pumps and one with a power rating one tier higher than that of the motor should be selected. Starting torque is an option that is easily overlooked; for loads with high inertia, the frequency converter may need to have a power rating several notches higher than that of the motor. Such as 3, cost-performance considerations when choosing a frequency converter; 4, options regarding after-sales service for frequency converters. After-sales service is a key factor in choosing a brand – imported brands offer reliable quality, higher prices, and good after-sales support, but the repair costs are very high once the warranty period has expired. The quality of domestic brands varies greatly; those of good quality are on par with imported brands, while those of poor quality are less reliable. The after-sales service is good; even after the warranty period has expired, the repair costs are reasonable.

First, check the motor’s rated power and rated current, then determine whether it is a constant-torque or variable-torque load. Also, find out what voltage is being supplied to the inverter. For the rest, consider communication, or whether to use a four-quadrant or two-quadrant approach, etc.

Select according to the current requirements of the process equipment

Based on the motor speed, power, etc. required by the process